1. Field of the Invention
The present invention relates to testing of filaments on being dispensed from a wound pack, and, more particularly, to the testing of an optical fiber from a wound pack which is contemplated for use in a data link to determine tensile forces generated in the fiber during dispensing as well as bending stiffness.
2. Description of Related Art
Filaments, and especially optical fiber filaments, are used in certain applications such as in missiles, for example, as a data link in which a length of a filament is wound onto a dispenser bobbin located aboard the missile connected to apparatus carried by the missile, the other end of which is interconnected with on-site apparatus. At launch, the optical fiber is dispensed maintaining the link between the apparatus via an optical signal transmitted along the fiber. As the desired speed for dispensing increases and the fiber diameter becomes smaller, the manner of dispensing must be carefully chosen in order to avoid direct breakage of the fiber or even microbending which has been found to produce deterioration of the optical signal. Prior to installation of use of a given dispenser, it is therefore advisable to test the dispenser under facsimile conditions in order to determine that the stressing and bending limits are not exceeded for the fiber.
There are existing machines for performing such filament tests and it has been found advisable in performing such tests to pull the filament through a substantial distance (i.e. 50 feet or more) to allow damping of the payout helix. Where there is a fast moving filament, and this is the usual case in a dispenser of the kind referenced, there is a substantial aerodynamic drag during the filament pullout which adds an additional tension load to the filament beyond that which would normally be expected to occur during actual payout from a moving vehicle. Accordingly, it has been found necessary that after passing through the pulling device a new helix must be introduced to promote a controlled deceleration of the fiber. In explanation, uncontrolled deceleration results in high speed collisions of the loops that cause signal attenuation as well as actual fiber breakage. Still further, controlling the deceleration is increasingly difficult as the filament diameter becomes less because of the corresponding decrease in bending stiffness.
One known present day apparatus for use in testing dispensing of a fiber optic cable is referred to as a pneumatic shoe capstan which establishes an air bearing having a groove within which a cushion of pressurized air is emitted for supporting the fiber optic cable located therein. The fiber optic cable can be pulled through the air bearing groove without effecting direct physical contact of the fiber with a material surface which considerably reduces the frictional drag that would be encountered with a conventional pulley. Although this known apparatus offers a substantial improvement over conventional frictional engagement apparatus, the problem of deceleration must be met successfully in order to prevent damage to the fiber. This requires additional equipment which is expensive. Also, having to pull the filament through a substantial distance poses a problem of aerodynamic drag which adds a tension load exceeding the expected performance requirements.